Different methods have been used to reinforce various acrylic polymers. For example, crosslinking the polymeric chains can impart greater shear strength and cohesive strength to the materials. This crosslinking can be chemical or physical. Chemical crosslinking can include the introduction of a monomer having multiple groups capable of undergoing polymerization reactions or multiple groups that react or interact with other groups on the polymeric chains. Physical crosslinking methods have included the introduction of another polymeric moiety that is linked to the main polymer chain but has the ability to phase separate from the main polymer and form its own domain within the polymeric material. When the polymeric material is an adhesive material, these phase separated polymeric moieties can be selected to have a higher glass transition temperature than the primary elastomeric polymer as described, for example, in U.S. Pat. Nos. 6,734,256 (Everaerts et al.), 7,255,920 (Everaerts et al.), and 5,057,366 (Husman et al.).
Bis-aziridine compounds have been used as chemical crosslinking agents in various polymer systems. Such compounds are described, for example, in U.S. Pat. No. 6,893,718 (Melancon et al.), German Patent No. 836,353 (Bestian), in an article of Bestian (J. Lieb. Ann. Chem., 566, 210-244 (1950)), in an article of Babenkova (J. of Applied Chemistry of the USSR, 40, 1715-1719 (1967)), and in an article of Kadorkina et al. (Bulletin of the Academy of Sciences of the USSR, 40, 780-783 (1991)).
Some aziridinyl-terminated polymers have been prepared as described, for example, in an article of Kobayashi et al. (Journal of Polymer Science: Part A: Polymer Chemistry, 43, 4126-4135 (2005)), Japanese Patent Publication JP4294369B2 (Kobayashi et al.), and European Patent Publication EP0265091A1 (Hertier et al.).